查找表中多余的重复记录，重复记录是根据单个字段（DocId）来判断

select * from TableName

where DocId in (select DocId from TableName group by DocId having count(DocId) > 1)

例二：

select * from TableName

where UserName in (select UserName from TableName group by TableName having count(TableName) > 1 )

可以查出表中UserName相同的记录

2、删除表中多余的重复记录，重复记录是根据单个字段（DocId）来判断，只留有DocId最小的记录

delete from TableName

where DocId in (select  DocId from TableName group by DocId  having count(DocId) > 1)

and DocId not in (select min(DocId) from  TableName group by DocId having count(DocId)>1)